#!/usr/bin/perl

use strict;
use warnings;
use Mojo::DOM;
use Mojo::File;

# read the xml file
my $source = Mojo::File->new( 'source.xml' );
my $xml = $source->slurp;

# use Mojo::Dom to parse the XML
my $dom = Mojo::DOM->new->xml(1)->parse( $xml );

# for each inline-formula id in the file
for my $e ( $dom->find('inline-formula[id]')->each ){
  # create file named value_of_id.mml
  my $file = "$e->{id}.mml";
  my $path = Mojo::File->new( $file );
  # write contents to file
  $path->spurt( $e->to_string );
}